arch: Changes MPU alignment to 128 when FPU_SHARING and MPU_STACK_GUARD

With our builds for Arm M7 we are selecting FPU_SHARING and
MPU_STACK_GUARD. For that setup, we have
ARM_MPU_REGION_MIN_ALIGN_AND_SIZE=64 and
MPU_STACK_GUARD_MIN_SIZE_FLOAT=128. So worst case scenario,
we are going to have stack that is 64-byte aligned and
128-byte guard at the bottom of the buffer.

Fixes: #83714

Signed-off-by: Maciej Kusio <rysiof@gmail.com>